Recently, the number of battery-driven electronic devices has increased with not only a demand for reduction in size, weight and power consumption of the electronic devices, but also with an increase in battery capacity. Moreover, data communication between devices within a near range has been practiced wirelessly in an increasing number of applications. Under such a situation, contactless power transmission techniques are also demanded in relation to electric power.
As disclosed in Japanese Unexamined Patent Application Publication No. 2008-206327, for example, a contactless charging system of related art is constituted by a power sending device including a primary coil disposed in a charging stand or the like, and by a portable electronic device including a secondary coil and a chargeable battery. A user places the portable electronic device on the power sending device. Upon the placement of the portable electronic device on the power sending device, the primary coil in the power sending device and the secondary coil in the portable electronic device are brought into a state under coupling through electromagnetic induction coupling (i.e., magnetic coupling). Hence electric power is supplied to the charging device side and the chargeable battery is charged.